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Abstract

A rigorous method of modeling the performance of metal-semiconductor-metal photodetectors (MSM-PD) that use several electromagnetic resonance (ER) modes and optical modes to enhance performance is presented. These ER and optical modes include surface plasmons, Wood-Rayleigh anomalies and vertical cavity modes. Five modeling algorithms are integrated together in a time-dependent way to model a 256 pseudo-random bit sequence (PRBS) of 850nm wavelength TM polarized light, the electromagnetic field distribution in the MSM-PD, quasi-static electric field, the charge carrier motion, and an algorithm to construct eye diagrams and analyze responsivity, inter-symbol interference (ISI) and bit error ratio (BER). We report on the use of a combination of ER and optical modes in channeling more than 83% of the incident light into the silicon even though 60% of the Si surface area is covered with metal contacts. Also, this channeled light is localized near the Si surface below the contact window. The absorption in the metal contacts, reflection, diffraction, electromagnetic field profiles, Poynting vector, photocurrent, eye diagrams, quality factors, responsivity and BER are calculated. Designs for Si MSM-PDs with a bandwidth of 100Gb/s, responsivities in the range of 0.05→0.30A/W and BERs in the range of 10-20→10-10 are described.

A schematic of the IEORA program. For each step in time (each of the 256 bits is divided into approximately 20 time steps), all five algorithms above are called on to perform their tasks as listed above.

The structural parameters for the Si MSM-PD that is analyzed in this work. One period of the structure is shown, from the MIDDLE of one contact to the MIDDLE of the next identical and identically surrounded contact.

Top Left: Ro and To for the Si-MSM-PD structure that is optimized to select a hybrid WR/CM mode. The structure is designed to have a slight misalignment of R0 and T0 because of the desirable field profile that is subsequently produced. Top Right: The Poynting vector showing that a large amount of energy is channeled around the electrical contacts and into the Si substrate. The groove with ε=2 shows increased energy channeling compared with the other groove with ε=1. This asymmetry of the groove dielectrics is introduced to inhibit HSPs. Bottom: Two graphs of the energy density showing a desirably high energy density between the contacts and close to the contact/Si interface. While the light localization near the contact/Si interface is significant, the expanded view shown in the bottom right plot shows that there is still some light that propagates deep into the Si that will reduce bandwidth and increase ISI and BER.

The PRBS Algorithm uses a m-stage shift register to obtain the bit sequence. The index k represents the kth bit. After each period of time, or output of one bit, the values in the registers are modified according to the equations shown in the figure.

A typical optical communication system including the four components: photodetector, transimpedance amplifier, limiting amplifier and clock data recovery block. The ISI will be evaluated at the input of the TIA.

Top Left: The eye diagram for a Si MSM-PD operating at 100Gb/s with an active layer depth of 0.5μm. Top Right: The dependence of responsivity and BER on the depth of the active layer. Bottom: The eye diagram for a Si MSM-PD operating at 100Gb/s with an active layer depth of 6μm. Both eye diagrams use the same y-axis units, illustrating the fact that the 6μm active layer device has higher responsivity but much increased noise and BER. For the device with 0.5μm active area thickness, the BER has a very low value of 10-20 but with a low responsivity of 0.06A/W, whereas for the device with 6μm active area thickness, the BER is a higher value of 10-9 but with a higher responsivity of 0.25A/W.